The present invention relates to a method and a device for processing a wire that is held at its ends.
After a wire is manufactured, in many cases the wire is fed into a rotating drum. Such a wire drum may contain wire lengths of up to several thousands of meters and can weigh up to about eighty kilograms.
In fully automatic wire-processing, the desired length of wire is pulled out of the top of the non-rotating wire drum by means of grippers and/or belt drives or roller drives.
Normally, wire-processing devices are fed with different types of wire from several wire drums which can be selected and changed according to need by programmed control. Active driving or rotation of the cable drums would be too cost-intensive, especially since different intermittent wire processes would make costly controlled wire stores necessary as compensation (see FIG. 9).
If, when the wire is pulled out of the wire drum, the wire cannot turn or relax into the longitudinal axis of the wire, twist builds up in the wire that depends on the internal and external diameter of the wire drum or on the momentary withdrawal diameter. For example, a 360° drum rotation and a withdrawal diameter of 400 mm results in a 360° twist in a pulled-out length of 1.25 meters assuming constant propagation of twist through the straightening track and the wire advancing device.
During wire advancing and wire-processing, twist is always built up in the wire when each end of the wire is held by grippers. The wire then can not freely untwist or relax by itself about the longitudinal axis of the wire. If only one end of a wire is held by means of grippers, no twist can build up in the longitudinal axis of the wire, and the wire can twist freely around its longitudinal axis while being advanced to length. The twist in the wire manifests itself negatively particularly if the wire-ends are fitted with contacts that are not fitted in housing compartments in a 1:1 sequence. When the wire bundle is stretched, it is easy for knots to form that can only be undone manually (see FIG. 1). Desirable, however, is a wire bundle according to FIG. 2. Even contactless wires of longer length that are taken out of the machine in bundled state tend to twist. The consequence is tangled wire in the wire bundle that also has to be untangled manually.
A wire of strands serving as an electric conductor has a certain number of individual wires and an insulation. In the field of electronics, for example 7 or 19 individual wires of copper are laid with a particular lay (see FIG. 3). Depending on the direction of lay, the lay is called left-hand lay (S-lay) or right-hand lay (Z-lay) (FIGS. 4 and 5).
Because of the special construction of a 19-strand wire, there are several different possible ways of laying (see FIGS. 6 and 7), four types being typical:
a) same direction of lay/same length of lay (unilay concentric);
b) same direction of lay/different length of lay (unidirectional concentric);
c) different direction of lay/same length of lay (equilay concentric); and
d) different direction of lay/different length of lay (conventional concentric).
After laying, by means of an extruder the wire is covered with an insulation which can be of greatly varying hardness and thickness depending on need.
If a wire with the aforesaid characteristics is now pulled through a straightening track of a wire-processing machine, the tensions of the individual wire strands can change and thereby greatly affect the overall twist (drum, wire) as a result of overlaying.